Transformer with amorphous alloy core having chip containment means

ABSTRACT

A transformer comprises a tank containing insulating liquid, and within the liquid there is an amorphous-alloy laminated core that comprises spaced-apart upper and lower yokes and two spaced-apart legs at opposite ends of the yokes. Coil structure surrounds the legs, locating the yokes outside the coil structure. Box-like enclosures primarily of electrical insulating material respectively enclose the yokes in positions outside the coil structure. The enclosure about the lower yoke is positioned to capture therein chips of amorphous alloy which might become detached from said core and fall toward the bottom of the tank.

This application is a continuation of application Ser. No. 810,664 filedDec. 19, 1985.

BACKGROUND

This invention relates to an electric transformer and, moreparticularly, to a transformer having a core of amorphous ferromagneticalloy.

Traditionally, the cores of electric transformers have been made ofgrain-oriented silicon steel laminations. In recent years, however,amorphous ferromagnetic alloy has been proposed for such use in order todecrease core operating losses. This amorphous alloy is available in theform of very thin strip material which is quite brittle, especiallyafter annealing. Using this strip material for core laminations, it isvery difficult to make a laminated amorphous alloy transformer corewithout some chipping or breaking of the edges of the core laminations.Most such chips can be removed during the manufacturing process, butthere is a chance that a small quantity will appear or be developedlater.

The presence of loose metal chips in a transformer is very undesirablesince such chips can deposit on and short out winding insulation and canreduce the dielectric strength of the insulating oil in the transformer.Either of these conditions can lead to a failure of the transformer.

OBJECTS AND SUMMARY

An object of my invention is to capture and contain any metal chipsdetached from the amorphous alloy core and unremoved during themanufacturing process, in a location where the chips will not producethe above described failures.

Another object is to provide simple, inexpensive, and effective meansfor capturing and containing such chips.

In carrying our the invention in one form, I provide a transformer thatcomprises a tank containing insulating liquid. Within the liquid thereis an amorphous alloy core comprising spaced-apart upper and lower yokesand two spaced-apart legs at opposite ends of the yokes. Coil structuresurrounds the legs, locating the yokes outside the coil structure. Abox-like enclosure primarily of electrical insulating material enclosesthe lower yoke in a position outside the coil structure and ispositioned to capture therein chips of amorphous alloy which mightbecome detached from said core and fall toward the bottom of the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to thefollowing specification in conjunction with accompanying drawings,wherein:

FIG. 1 is a front elevational view, partly in section and partlyschematic, of a core-type transformer embodying one form of myinvention.

FIG. 2 is an end view of the core and coil assembly of the transformerof FIG. 1.

FIG. 3 is a simplified sectional view taken along the line 3--3 of FIG.1.

FIG. 4 is an enlarged detailed view taken along the line 4--4 of FIG. 3.

FIG. 5 is a front elevational view, partly in section and partlyschematic, of a shell-type transformer embodying one form of myinvention.

FIG. 6 is a plan view of the assembly of FIG. 5.

FIG. 7 is a sectional view along the line 7--7 of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIG. 1, the transformer shown therein is a distributiontransformer comprising a metal tank or enclosure 12 containing aninsulating liquid 14. Within the insulating liquid is the core and coilassembly 15 of the transformer.

This assembly 15 comprises two coils 17 and 18 and a wound laminatedcore 20 of amorphous ferromagnetic alloy linked to the coils. Prior toits incorporation into assembly 15, the core 20 is made from amorphousalloy in strip form, such as that commercially available from AlliedCorporation as its Metglas 2506-S2 material. The core may be made in anynumber of different ways, but the illustrated core is preferably made bywinding the amorphous strip into an annular form (not shown), cuttingthe annular form along a single radial line thereby creating separatelaminations, and then reassembling the laminations to form a secondannulus (not shown) with distributed gap joints in a localized region ofthe second annulus. Then the second annulus is formed into the generallyrectangular shape shown in FIG. 1, so that it comprises fourintegrally-connected sides consisting of two yokes 21 and 22 and twolegs 23 and 24 at opposite ends of the yokes, with the joints (shown at25) being located in yoke 22. After this forming step, the core isannealed to relieve the stresses resulting from the earlier fabricationsteps. Then, a thin layer of adhesive bonding agent, shown at 26 in FIG.1, is applied to the lateral edges of the laminations in the upper yoke21 and in the two legs 23 and 24. The lower yoke 22 and the cornerregions of the core at opposite ends of the lower yoke are kept free ofthis bonding agent in order to permit ready displacement of these coreportions during subsequent lacing of the core into the coils. Afterbonding, the joints 25 are opened, and the portions of the yoke atopposite sides of the joints 25 are displaced into positions ofalignment with the legs 23 and 24 to convert the core into a U-shapedstructure that can be easily laced into the two coils 17 and 18, whichhad been pre-wound in a conventional manner.

Lacing is accomplished by inserting one leg of the above-describedU-shaped core structure into the central passageway of pre-wound tubularwinding 17 and the other leg into the central passageway of pre-woundtubular winding 18. Thereafter the displaced yoke portions of the coreare returned to their closed-joint positions of FIG. 1 to remake thejoints 25. A sleeve of insulating material, preferably a suitable kraftpaper, is then applied to the yoke 22 about the region of joints 25.This sleeve is shown at 30 in FIG. 1. Preferably, the sleeve is formedfrom a sheet of kraft paper which is snugly wrapped around the jointregion, following which its ends are taped together.

Before the core is laced into the coils as above described, twochannel-shaped insulating members 34 and 36, referred to as coreshields, are respectively applied to the coils in the locations shown inFIG. 1. The horizontal flanges of these channel-shaped members act asspacers which prevent the inner surfaces of the yokes 21 and 22 fromdirectly contacting the edges of coils 17 and 18 and thus reducing thedielectric strength of the coil structure. The insulating members 34 and36 also space and provide insulation between the juxtaposed outerperipheries of the coils 17 and 18. It is to be understood that the highvoltage windings of the transformer are located in the radially outerregion of each coil 17 and 18, and it is therefore important to maintaina high dielectric strength of the insulation in these regions.

After the core 20 is thus laced into the coils 17 and 18, two thin endpanels 38 of suitable insulating material such as kraft paper arerespectively inserted into the passageways of coils 17 and 18 adjacentthe outer surface of the core legs 23 or 24 already positioned therein.These passageways are of a rectangular cross-section, and this allowsthe panels 38 to be flat sheets. It will be noted that the panels 38 aresufficiently long that their upper and lower ends extend well beyond theupper and lower ends of the coils 17 and 18, respectively. The purposeof these sheets, or panels 38, will soon be described.

As a next step in the assembly process, two box-like enclosures 40 and42 are applied to the portions of the core that are then located outsidethe coils. The bottom enclosure 40 has four vertically-extending walls44 disposed in a rectangular pattern and a bottom wall 46. The top ofthis bottom enclosure 40 is open, and this allows the bottom yoke 22 ofthe core to enter and to fit within the enclosure 40. The upperenclosure 42 is substantially the same as the bottom enclosure 40 exceptthat it is inverted. The open bottom of the upper enclosure 42 allowsthe upper yoke 21 to enter and to fit within the upper enclosure.

It will be noted that the end panels 38 at their top and bottom endsextend into the enclosures 40 and 42. The panels 38 tend to block anyopenings (such as might possibly be present at 47) between the lateralend walls of the enclosures 40, 42, and the end surfaces of the coils 17and 18.

The next step in the assembly process is to incorporate horizontal topand bottom clamping plates 50 and 52 between which the coil structure17, 18 is clamped. These horizontal plates 50 and 52 are separated fromthe coil structure 17, 18 by vertically-extending rigid plates 54 ofinsulating material. At the upper end of the coil structure 17, 18, twoof these plates 54 are disposed perpendicular to the upper horizontalplate 52 and on opposite sides of the upper enclosure 42, as best seenin FIG. 2. At the lower end of the coil structure 17, 18, two of theplates 54 are disposed perpendicular to the lower horizontal plate 50and on opposite sides of the lower enclosure 40. These vertical plates54 are disposed closely adjacent the side walls of the enclosures 40 and42, respectively, and thus tend to impede flow through any cracks oropenings present between the side walls and the end surfaces of thecoils 17 and 18.

The two horizontal plates 50 and 52 are forced toward each other byforces developed through a flexible clamping band 58, preferably ofsteel, that is placed in tension. As best seen in FIG. 1, this bandextends upwardly through two openings 60 in the bottom horizontal plate50 and through two slots 62 in the bottom wall of the lower enclosure40, then upwardly through the passageways of the coils 17 and 18, thenthrough slots 64 in the end walls of the upper enclosure 42 and thenthrough openings 66 in the upper horizontal plate 52. This band 58,which is looped around the portion of bottom horizontal clamping plate50 between openings 60, is suitably tightened to place it under tension,and suitable clips 68 are applied to its free ends to hold it in itstightened state.

The horizontal clamping plates 50, 52 being forced together by tensileforces in band 58, clamp the coil structure 17, 18 between thevertically-extending insulating plates 54. The vertically-extendingplates 54 have sufficient height to avoid applying compressive forcesvia the enclosures 40 or 42 from the clamping plates to the core 20.

As pointed out in the introductory portion of this specification, theamorphous ferromagnetic alloys that are available today are ratherbrittle and occasionally break and chip, especially along the edges ofany thin strips composed thereof. The illustrated core is made of suchstrip, and it is therefore possible for some chipping thereof to occurat the edges of such strip, which are located along the core face facingthe viewer in FIG. 1 and the parallel back face, as well as at thejoints 25. The adhesive coating at 26 provides significant protectionagainst such chipping and helps to contain chips that are developed, butit is not completely effective in this respect in the bonded areas and,moreover, has little effect in the areas not covered by the coating 26,e.g., along the bottom yoke 22 and at the joints 25. Most such chips canbe removed during the manufacturing process, but there is a chance thatsome can appear or be developed later.

The presence of loose chips especially in the insulating liquid 14 isvery undesirable because these chips may deposit on the coil insulationand such metal deposits can short out insulation and cause a dielectricfailure. Moreover, the presence of metal chips in the insulating liquidimpairs the dielectric strength of the insulating liquid itself, andthis can lead to a dielectric failure in regions of the insulatingliquid where there are high electric stresses.

The box-like enclosures 40 and 42 provide significant protection againstsuch dielectric failures. Any chips that are detached from the core andwhich fall toward the bottom of the tank 12 are intercepted by andcaptured within the lower enclosure 40. Some of the finer chips maybecome entrained in the oil and may tend to move with the oil as itcirculates between the bottom and top of the tank as it is heated by thetransformer losses in the region of the core and coil assembly and as itcools upon entry into regions remote from the core and coil assembly.The upper enclosure 42 acts as sort of a filter or baffle to block thesechips from leaving the core region and from escaping into thesurrounding oil regions or onto the high voltage surfaces of the coils,which are located adjacent their outer peripheries.

The core of the illustrated transformer is connected to ground bysuitable means (not shown) and is therefore at ground potential. Byconfining detached metal chips to the region immediately around thecore, the chips are confined for the most part to a region of relativelylow electric stress, where their potential for causing dielectricfailures is much less. Referring to FIG. 3, it will be seen that thebox-like enclosure 42 closely conforms to the rectangular outerperimeter of the core 20 where the core intersects the upper surface ofcoil structure 17, 18, and thus is capable of providing an effectivebarrier against escape of chips from the interior of enclosure 42. Itwill be seen in FIG. 3 that most of the outer peripheral region, whichis the high voltage region, of each coil 17 or 18 is outside theperimeter of the box-like enclosure 42 and is thus well isolated fromany chips in the interior of enclosure 42. As will be apparent from FIG.3, there is a limited portion of the outer peripheral region of eachcoil that is disposed within the enclosure 42. But this limited portionis covered by the upper flanges of the insulating core shields 34 and36, and any chips resting in this location are separated from the highvoltage winding of the coils by these insulating flanges, thus reducingthe chances for any resulting dielectric problems.

To accommodate these flanges of core shields 34 and 36 withoutcompromising the close fit between the edges of vertical plates 54 andthe upper surface of the coil structure 17, 18, the lower edges of theplates 54 are provided with notches for receiving these flanges. Onesuch notch is shown at 65 in FIG. 4, where it can be seen that the notchclosely conforms with the outer outline of these flanges to minimizegaps in this region through which chips could escape from the interiorof enclosure 42. The lower edges of the walls of enclosure 42 can beprovided with similar notches for receiving flanges 34 and 36 and thusimproving the fit between these edges and the upper surfaces of coils 17and 18.

Similar notches are also present in the upper edges of the lower plates54 and the sidewalls 44 of the lower enclosure 40 for this same purpose.

While I have shown the invention applied to a transformer with acut-type core, it is to be understood that it is also applicable to thetype core that has no cut or joint therein.

This invention in its broader aspects is also applicable to shell-typetransformers, as well as to transformers of the core-type, which aredepicted in FIGS. 1-4. FIGS. 5 and 6 show a shell-type transformer thatcomprises two cores 70 and 72, each made from amorphous metal strip andeach comprising spaced-apart upper and lower yokes 74 and 76 and twolegs 78 and 80 at opposite ends of each yoke. Surrounding one leg 78 ofeach core is coil structure 82. The other legs 80 of the two cores arelocated outside the coil structure and at diametrically opposedlocations on the coil structure. The yokes 74 and 76 are also locatedoutside the coil structure 72.

The upper yokes 74 are enclosed by a first box-like enclosure 84 ofinsulating material that is supported on the top surface 85 of the coilstructure 82. The lower yokes 76 are enclosed by a second box-likeenclosure 88 of insulating material that is supported at the lowersurface 89 of the coil structure 82.

Enclosing each of the outer legs 80 of the cores is a panel 90 ofU-shaped horizontal cross-section that is suitably supported in theposition shown. Each of these panels 90 is longer than the core leg 80which it encloses and extends at its upper end into the upper enclosure84 and at its lower end into the lower enclosure 88. Each panel issnugly received by the enclosure into which it extends, and this assuresthat any gaps between the panel and the enclosure will be small and willnot readily allow the passage therethrough of any chips.

Any chips that are detached from the amorphous metal cores 70 and 72will be captured and contained within the composite enclosure structuremade up of enclosures 84 and 88 and panels 90, thus substantiallyreducing their chances for depositing on the high voltage portion of thecoil structure 85 and for becoming entrained in the surrounding oil. Thecore enclosing structure 84, 88, 90 closely envelopes those portions ofthe core structure 70, 72 that are outside the coil structure 82 andthus maintains the chips in a location where they have a low likelihoodof causing dielectric problems.

The transformer of FIGS. 5-7 uses essentially the same coil support andclamping means as that of FIGS. 1-4. In this respect, top and bottomhorizontal clamping plates 50 and 52 are provided, and a U-shaped band58 under tension extends between these plates to force them together.Force-transmitting plates 54 at opposite sides of each of the enclosures84 and 88 transmit clamping force from the horizontal plates 50 and 52to the coil structure 82. Since parts 50, 52, 54, and 58 are generallythe same in the two transformers, they are shown only partially in FIGS.5 and 6.

While I have shown and described a particular embodiments of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects; and I, therefore, intend herein tocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:
 1. In a transformer that comprises a tank containinginsulating liquid,(a) a core within said liquid comprising spaced-apartupper and lower yokes and two spaced-apart legs at opposite ends of saidyokes, the core comprising superposed laminations of amorphousferromagnetic alloy, (b) coil structure surrounding said legs, (c) saidyokes being located outside said coil structure, (d) a box-likeenclosure primarily of electrical insulating material enclosing saidlower yoke in a position outside said coil structure, (e) said enclosurebeing positioned to capture therein chips of amorphous alloy which mightbecome detached from said core and fall toward the bottom of said tank.2. The apparatus of claim 1 in which said enclosure closely conforms tothe perimeter of said core where the core intersects the lower surfaceof said coil structure.
 3. The apparatus of claim 1 in combination withan additional box-like enclosure primarily of electrical insulatingmaterial enclosing said upper yoke and located in a position outsidesaid coil structure.
 4. The apparatus of claim 3 in which saidadditional enclosure closely conforms to the perimeter of said corewhere the core intersects the upper surface of said coil structure. 5.In the transformer defined in claim 1,(a) bottom and top clamping platesrespectively located at opposite ends of said core; (b) means forforcing said plates toward each other; (c) means for transmitting forcebetween said plates and said coil structure thereby clamping said coilstructure between said plates; and (d) said box-like enclosure beinglocated between said bottom clamping plate and said coil structure. 6.The apparatus of claim 1 in which said core is made of amorphous alloystrip having edges located at the side faces of said core, and anadhesive bonding layer covers most of the area of said side faces andthereby inhibits the development and release of metal chips from thecovered area.
 7. The apparatus of claim 5 in combination with anadditional box-like enclosure enclosing said upper yoke and located in aposition outside said coil structure and between said upper clampingplate and said coil structure.
 8. The apparatus of claim 1 in which:(a)said lower yoke contains joints; and (b) a cover of insulating materiallocated within said enclosure closely surrounds said lower yoke andcovers said joints to capture chips of amorphous alloy which might bedetached from the core in the region of said joints.
 9. The apparatus ofclaim 1 in which:(a) said coil structure has a passageway therethroughthat receives one of said legs, said core has an outer peripherypartially located within said passageway, and said enclosure has wallsextending into close proximity with said coil structure; (b) a sheet ofinsulating material is located adjacent said outer periphery and withinsaid bore, and (c) said sheet extends from said passageway into saidbox-like enclosure closely adjacent one of the walls of said enclosure,and is thus in a position to inhibit the flow of liquid through anyopening between said one wall and said coil structure.
 10. The apparatusof claim 5 in which:(a) said force-transmitting means of (c), claim 5,comprises insulating structure located outside said box-like enclosureand between said bottom clamping plate and said coil structure, and (b)said insulating structure is located closely adjacent predeterminedwalls of said enclosure and in a position to inhibit the flow of liquidthrough any opening between said predetermined walls and said coilstructure.
 11. The apparatus of claim 1 in which said core is at groundpotential and said enclosure closely encloses said core so that thespace within said enclosure is in a region of relatively low electricalstress within said transformer.
 12. In a shell-type transformer thatcomprises a tank containing insulating liquid,(a) two cores within saidliquid, each core comprising spaced-apart upper and lower yokes and twospaced-apart legs at opposite ends of said yokes, each core furthercomprising superposed laminations of amorphous ferromagnetic alloy, (b)coil structure surrounding one leg of each core and located in aposition between the other two legs of said two cores, (c) said yokesand said other two legs being located outside said coil structure, (d) abox-like enclosure primarily of electrical insulating material enclosingsaid lower yokes in a position outside said coil structure and beingpositioned to capture therein chips of amorphous metal which mightbecome detached from said core and fall toward the bottom of said tank,(e) an additional box-like enclosure primarily of electrical insulatingmaterial enclosing said upper yokes in a position outside said coilstructure, and (f) panels primarily of insulating material respectivelydisposed about the other legs of said cores and extending between saidenclosures.
 13. The apparatus of claim 12 in which,(a) said firstbox-like enclosure closely conforms to the perimeter of the two corestaken together where said two cores intersect the lower surface of saidcoil structure, and (b) said additional box-like enclosure closelyconforms to the perimeter of the two cores taken together where the twocores intersect the upper surface of said coil structure.
 14. In thetransformer of claim 12,(a) bottom and top clamping plates respectivelylocated at opposite ends of said two cores, (b) means for forcing saidplates toward each other, (c) means for transmitting force between saidplates and said coil structure thereby clamping said coil structurebetween said plates, and (d) said box-like enclosures being respectivelylocated between said bottom clamping plate and said coil structure andsaid top clamping plate and said coil structure.